Rats - I was right the first time: there's a messy problem with snapshots.
The problem is that the parent of the child that you're about to update in place may *already* be in one or more snapshots because one or more of its *other* children was updated since each snapshot was created. If so, then each snapshot copy of the parent is pointing to the location of the existing copy of the child you now want to update in place, and unless you change the snapshot copy of the parent (as well as the current copy of the parent) the snapshot will point to the *new* copy of the child you are now about to update (with an incorrect checksum to boot). With enough snapshots, enough children, and bad enough luck, you might have to change the parent (and of course all its ancestors...) in every snapshot. In other words, Nathan's approach is pretty much infeasible in the presence of snapshots. Background defragmention works as long as you move the entire region (which often has a single common parent) to a new location, which if the source region isn't excessively fragmented may not be all that expensive; it's probably not something you'd want to try at normal priority *during* an update to make Nathan's approach work, though, especially since you'd then wind up moving the entire region on every such update rather than in one batch in the background. - bill This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
